Nystagmus is involuntary movement of the eyes. The nystagmus of human subjects will vary with certain disorders, principally disorders of the inner ear. It is known that the eye acts as an electrical dipole, with the cornea positive and the retina negative. The electric axis of the dipole is thus coincident with the optical axis of the eye. Electrodes placed on the skin adjacent the eyes will pick up voltages from the electric dipole, and these voltages will vary as does the eye movement. For example, electrodes of the temples will pick up voltages caused by horizontal eye movement which can be amplified and recorded to form a record of eye movement, both voluntary and involuntary. Instruments designed to pick up and record such voltages are known as electronystagmograph (ENG) machines. ENG machines have found extensive use in the prior art as an aid in diagnosing various ailments associated with the inner ear, for example, vertigo, Meniere's disease, lesions of the labyrinth and neurological ailments such as multiple sclerosis. In diagnosing vertigo, or in verifying a complaint of vertigo in compensation cases, the nystagmus of the subject is measured during positional or static tests in which the subject is placed in various positions. If vertigo is produced in any position its latency and fatigability is measured by repeated tests in this position. Active tests include spinning the subject in the two directions while seated in a rotatable chair with abrupt stops. This will produce vertigo of a few seconds duration in a normal subject, but longer periods indicated by the nystagmus recorded on the ENG for subjects with vertigo. Stimulatory or caloric tests involve irrigating the ear with 21/2 cc of cold water. The water is removed after 20 seconds and the subject placed on his back with his head elevated 30.degree. from the horizontal. The eye movement caused by the effect of the chilling of the fluids within the vestibular system is recorded on the ENG and compared to the normal duration of such eye movement to indicate disorders of this system.
ENG machines have also been used to measure the effect of anti-motion sickness remedies which suppress the normal function of the vestibular system in maintaining balance.
It has been known that drugs can in a general manner affect the nystagmus and hence workers in this field have usually taken their patients off medication before making tests involving nystagmus, such as those described above.
The present invention on the other hand, takes advantage of the effect of drugs, especially dangerous narcotic drugs, on the waveform to provide a non-invasive technique for diagnosing ingestion of such drugs.
The method of recording nystagmus by measuring the electrical field around the eye was first presented by Schott in 1922 and again by Meyers in 1929. Although Meyers thought that it was actually measuring the action potentials of the extraocular muscles, it was later discovered that the corneo-retinal potential difference detected at the lateral orbital areas are proportional to the angle of movement of the eyes.
The ENG has been used since that time to aid in the diagnosis and treatment of the cause of vertigo and other ailments, as explained above.
The problems of driving while under the influence of drugs and/or alcohol are well documented in the literature. Studies have shown that 10 to 35% of serious injury accidents involve persons whose blood alcohol concentration (BAC) is 100 mg/100 ml or higher. It has been estimated that from 40 to 50% of all fatally injured drivers have had blood alcohol concentrations that exceed the legal limit. Another study has shown that a large percentage of drivers arrested for intoxication in Dallas County over a two year period were under the influence of drugs such as diazepam, methaqualone, and barbiturates in addition to alcohol. These findings have pointed up the necessity for developing an objective, practical method of ascertaining the quality and quantity of drugs in drivers accused of being "under the influence". The controversial results of subjective clinical examination and blood alcohol tests reported by Rasch in a 1969 issue of the Journal Blutalkohol, 28:11-21, have encouraged many investigators to attempt to set up a model for ascertaining the degree of impairment related to alcohol intake using objective methods. Nystagmus tests have been found to be one of the most reliable objective methods for this purpose. Penttila's model is probably the best known, in which he devised an optimal model for determining degree of impairment using 494 subjects after testing over 100 models containing several different subtests. Using regression analysis, nystagmus tests were found to be most valuable. The final results yielded a value of 42% for nystagmus tests in the overall model for determining the effects of alcohol on the sensory motor system of an individual. The work of Penttila and his co-workers is reported in the J. of Medicine, Science and Law, vol. 16, pp. 95-103, and in Blutalkohol, 12:24-38, 1975.
Various qualitative studies have been performed using the ENG to demonstrate the effects of alcohol on the peripheral and central nervous systems. These effects have ranged from decrease in intraocular pressure and deterioration of tracking eye movement to changes in dynamic visual acuity, sinusoidal tracking, oculomotor tracking and peripheral gaze nystagmus.
Umeda and Sakata in 1978, in attempting to establish a pattern of alcohol affects, found that in normal subjects, alcohol affects the oculomotor system in the following order: caloric eye pattern tracking difficulties, positional alcohol nystagmus (PAN), eye tracking pattern difficulties, and finally alcohol gaze nystagmus abnormalities. Their research indicates that alcohol affects the cerebellum first, that visual suppression function is affected by alcohol, and that positional alcohol nystagmus (PAN) appears at a relatively early stage after the consumption of alcohol. It has been fairly well established that PAN I appears within 15 to 30 minutes in normal subjects with even a small amount of alcohol ingestion. See the following articles on this subject: Howells, British Medical Journal, 1:1405-1406, 1956; Fregly et al, Quarterly Journal of Studies of Alcohol, 28:11-21, 1967; Ey, Bericht Der Deutschen Opthalmologischen Gesellschaft, 65:349-353, 1964; Gottesberg, Medizinische Welt, 17:429-432, 1943; Loos et al, Blutalkohol, 16:321-329, 1979; Aschan et al, Quarterly Journal of Studies of Alcohol, 17:381-405, 1956. In that last mentioned article, Aschan and his co-workers report that PAN I has been measured at blood alcohol levels as low as 0.38 per mil. PAN I is the stage in which the person is initially affected by the alcohol. In this stage the nystagmus beats in the direction in which the head is positioned.
In studies which required the subjects to perform tasks to assess the degree of motor impairment, the degree of nystagmus appears to be a better indicator than blood alcohol levels. See the above-cited articles, of Howells, Fregly et al, Gottesberg, Loos et al, and Penttila et al, as well as Heifer in Blutalkohol, 13:66-75, 1976; and Rauscke, Medizinische, Stuttgart, 12:460-465, 1958. Howells found that in every case, an increase of reaction time was evidenced with the appearance of nystagmus, indicating a parallel impairment of the central nervous system. Fregly reports that in measuring degree of ataxia in persons who had imbibed alcohol, ataxic responses were in very close agreement with the intensity of PAN I. Maximum ataxia was observed sooner than maximum blood alcohol levels, and the ataxia improved during the time when blood alcohol remained high. Fregly et al report in the above-cited article that nystagmus most often begins about half an hour after the beginning of intoxication, while blood alcohol levels peak after one hour, thus indicating a lack of correlation between blood alcohol level and the time of maximum impairment. The close relationship between sensory motor impairment and the appearance of nystagmus can also be seen in the Loos et al study, in which peaks in post rotary fixation nystagmus occurred 8 minutes after imbibing alcohol, sensory motor impairment peaked in 19 minutes, and breath alcohol peaked in 40 minutes after the end of drinking.
Although the value of the ENG in determining degree of impairment related to alcohol intake is well known as evidenced by the articles discussed above, its use with other drug intake for qualitative diagnostic purposes has not yet been appreciated by the scientific community.
The effects of certain drugs on the quick component of vestibular nystagmus has been reported by several investigators, see for example, Anderson, et al, Neuroloqy, 8:741, 1958; Bender et al, Progress in Neurology and Psychiatry, 10:201, 1955; Jatho, Z., J. of Laryngology Rhinology and Otology, 44:1, 1965; Jongkees et al, Acta Physiologica Pharmacologica Neerlandica, 9:240-275, 1960; McCabe, Laryngoscope, 75:1619, 1965; Nathanson et al, Medical Clinics of North America, 701, May, 1958; and Palve et al, European Journal of Clinical Pharmacology 13:345-350, 1978. The influence of drugs and their action in combination with alcohol has also been studied to some degree by researchers. See for example, Mattila et al, Archives Internationales de Pharmacodynamie et de Therapie, 234, 236-246, 1978; Bochenek et al, Acta Medica Polona, 15:117-126, 1974; Tomits, Ful Orr Gegegyogyaszat, 8:26-30, 1962; Goldberg, Quarterly Journal of Studies of Alcohol, Supp. 1, 37-56, 1961. However, there is no indication in the literature that any direct method for specific diagnostic purposes, such as the method of the present invention, has been used or suggested by workers in this field, or that the waveforms have been specifically identified.
The objective of the studies which lead to the present invention were to determine if specific ENG printouts of waveforms could be obtained for different drugs for purposes of drug identification and to qualitatively analyze the effects of relatively small amounts of alcohol on the vestibular system.